Apparatus for metering at least one type of electrical power over a predetermined range of service voltages

ABSTRACT

Methods and apparatus for supplying power for use in metering electrical energy over a wide range of voltages with a single meter are disclosed. The wide ranging meter includes a processing unit for processing divided input voltage and a current component in order to determine electrical energy metering values. The processing unit is operable in response to supply voltages. A power supply, connected to receive the undivided voltage component, generates the supply voltages over the wide dynamic range. It is especially preferred for the power supply to include a transformer having first, second and third windings, wherein the undivided voltage component is provided to the first winding and wherein the second winding defines the output of the power supply. A switching member is connected to the first winding for permitting and preventing the flow of current in response to a control signal. A control member generates the control signal in response to the output of the power supply. It is also preferred for the control signal to disable the witch member. It is further preferred for the power supply to include a voltage blocking clamp, connected to the transformer for blocking the voltage applied to the transformer. It is still further preferred for an oscillator to be used to generate an oscillating signal for switching the switching member ON and OFF so that the switching member is provided a substantially constant OFF time.

RELATED APPLICATION DATA

This application is a Continuation of application Ser. No. 10/076,990filed Feb. 15, 2002 now abandoned, which is a Continuation of Ser. No.09/781,501 filed Feb. 12, 2001, which is a Divisional of Ser. No.09/047,479 filed Mar. 25, 1998, now U.S. Pat. No. 6,229,295, issued May8, 2001, which is a Continuation of Ser. No. 08/478,605 filed Jun. 7,1995, now U.S. Pat. No. 5,903,145, issued May 11, 1999, which is aContinuation of Ser. No. 08/384,398, filed Feb. 3, 1995, now U.S. Pat.No. 5,457,621, issued Oct. 10, 1995, which is a Continuation of Ser. No.08/259,116 filed Jun. 10, 1994 (now abandoned), which is a Continuationof Ser. No. 07/839,967 filed Feb. 21, 1992 (now abandoned).

FIELD OF INVENTION

The present invention relates generally to the field of electric utilitymeters. More particularly, the present invention relates to electronicutility watthour meters or meters utilized to meter real and reactiveenergy in both the forward and reverse directions.

BACKGROUND OF THE INVENTION

Electric utility companies and power consuming industries have in thepast employed a variety of approaches to metering electrical energy.Typically, a metering system monitors power lines through isolation andscaling components to derive polyphase input representations of voltageand current. These basic inputs are then selectively treated todetermine the particular type of electrical energy being metered.Because electrical uses can vary significantly, electric utilitycompanies have requirements for meters configured to analyze severaldifferent nominal primary voltages. The most common of these voltagesare 120, 208, 240, 277 and 480 volts RMS. Presently, available metershave a different style for each of these applications, bothelectro-mechanical and electronic. This forces the electric utilitycompanies to inventory, test and maintain many different styles ofmeters. Consequently, a need exists for reducing the number of metertypes a utility need inventory by providing a meter capable of operationover a wide dynamic range.

The problem of wide amperage dynamic range was addressed in U.S. Pat.No. 3,976,941—Milkovic. It was there recognized that solid stateelectronic meters were becoming more desirable in metering applications,however, such solid state meters had a critical drawback in theiramperage dynamic range. An effort was described to improve the amperagedynamic range of solid state meters so that such meters would beoperationally equivalent to prior electromechanical meters. The problemwith such meters, however, was their failure to address the multiplevoltage situation. Utility companies utilizing such meters would stillbe forced to inventory, test and maintain many different styles ofmeters in order to service the various voltages provided to customers.

It has been recognized in various meter proposals that the use of amicroprocessor would make metering operations more accurate. It will beunderstood, however, that the use of a microprocessor requires theprovision of one or more supply voltages. Power supplies capable ofgenerating a direct current voltage from the line voltage have been usedfor this purpose. Since electric utility companies have requirements forvarious nominal primary voltages, it has been necessary to provide powersupplies having individualized components in order to generate themicroprocessor supply voltages from the nominal primary voltage.

Consequently, a need exists for a single meter which is capable ofmetering electrical energy associated with nominal primary voltages inthe range from 96 to 528 volts RMS. Applicants resolve the aboveproblems through the use of a switching power supply and voltagedividers. It will be recognized that switching power supplies are known.However, the use of such a power supply in an electrical energy meter isnew. Moreover, the manner of the present invention, the particular powersupply construction and its use in an electrical energy meter is novel.

It will also be noted, in order to solve the inventory problem,designing a wide voltage range meter in the past involved the use ofvoltage transformers to sense line voltage. A significant problemassociated with the use of such transformers was the change in phaseshift and the introduction of non-linearities that would occur over awide voltage range. It was not to remove such a widely changing phaseshift or to compensate for the non-linearities.

Consequently, a need still exists for a single meter which is capable ofmetering electrical energy associated with nominal primary voltages thatalso minimizes phase shift in the voltage sensors over a wide voltagerange.

SUMMARY OF THE INVENTION

The present invention is directed to a power supply for an apparatus formetering at least one type of electrical power over a predeterminedrange of service voltages supplied by electrical service providers,where the apparatus comprises a voltage input circuit connected toreceive a voltage component, and a processing unit. The power supplycomprises a surge protection circuit which receives an input voltage, arectifier circuit which receives an alternating current voltage from thesurge protection circuit and outputs a rectified direct current voltage,a transformer which receives the rectified direct current voltage at afirst winding so that current flows through the first winding, and asecond winding defines an unregulated output voltage of the powersupply, a switching device for permitting and preventing the flow ofcurrent through the first winding in response to a control signal, and acontroller for generating the control signal based on the voltage acrossthe third winding. The control signal output by the controller operatesto disable the switching member.

According to another feature of the present invention, the output of thepower supply is input to a linear regulator, which outputs a regulatedvoltage. The regulated voltage is less than the output voltage, and theregulated voltage is output to a precision voltage reference generator.The unregulated voltage is input to the apparatus to determine thepresence of a power fail condition.

According to yet another feature, the power supply comprises anon-volatile supply, and the regulated voltage is input to thenon-volatile supply, such that the apparatus is switched to thenon-volatile supply when the regulated voltage is not present.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood, and its numerousobjects and advantages will become apparent to those skilled in the artby reference to the following detailed description of the invention whentaken in conjunction with the following drawings, in which:

FIG. 1 is a block diagram of an electronic meter constructed inaccordance with the present invention;

FIG. 2 is a schematic diagram of the resistive dividers shown in FIG. 1;

FIG. 3 is a schematic diagram of the linear power supply shown in FIG.1;

FIG. 4 is a block diagram of the power supply shown in FIG. 1;

FIG. 5 is a schematic diagram of the control and switching members shownin FIG. 4;

FIG. 6 is a schematic diagram of the startup/feedback shown in FIG. 4;and

FIG. 7 is a schematic diagram of the voltage clamp shown in FIG. 4.

DETAILED DESCRIPTION

A new and novel meter for metering electrical energy is shown in FIG. 1and generally designated 10. It is noted at the outset that this meteris constructed so that the future implementation of higher levelmetering functions can be supported. Meter 10 is shown to include threeresistive voltage divider networks 12A, 12B, 12C: a first processor—anADC/DSP (analog-to-digital converter/digital signal processor) chip 14:a second processor—a microcontroller 16 which in the preferredembodiment is a Mitsubishi Model 50428 microcontroller: three currentsensors 18A, 18B, 18C; a 12V switching power supply 20 that is capableof receiving inputs in the range of 96–528V; a 5V linear power supply22: a non-volatile power supply 24 that switches to a battery 26 when 5Vsupply 22 is inoperative; a 2.5V precision voltage reference 28; aliquid crystal display (LCD) 30; a 32.768 kHz oscillator 32; a 6.2208MHz oscillator 34 that provides timing signals to chip 14 and whosesignal is divided by 1.5 to provide a 4.1472 MHz clock signal tomicrocontroller 16; a 2 kByte EEPROM 35; a serial communications line36; an option connector 38: and an optical communications port 40 thatmay be used to read the meter. The inter-relationship and specificdetails of each of these components is set out more fully below.

It will be appreciated that electrical energy has both voltage andcurrent characteristics. In relation to meter 10 voltage signals areprovided to resistive dividers 12A–12C and current signals are inducedin a current transformer (CT) and shunted. The output of CT/shuntcombinations 18A–18C is used to determine electrical energy.

First processor 14 is connected to receive the voltage and currentsignals provided by dividers 12A–12C and shunts 18A–18C. As will beexplained in greater detail below, processor 14 converts the voltage andcurrent signals to voltage and current digital signals, determineselectrical energy from the voltage and current digital signals andgenerates an energy signal representative of the electrical energydetermination. Processor 14 will always generate a watthour delivered(Whr Del) and, watthour received (Whr Rec), depending on the type ofenergy being metered, will generate either a volt amp reactive hourdelivered (Varhr Del)/a volt amp reactive hour received (Varhr Rec)signal or volt amp hour delivered (Vahr Del)/volt amp hour received(Vahr Rec) signal. In the preferred embodiment, each transition onconductors 42–48 (each logic transition) is representative of themeasurement of a unit of energy. Second processor 16 is connected tofirst processor 14. As will be explained in greater detail below,processor 16 receives the energy signal(s) and generates an indicationsignal representative of said energy signal.

It will be noted again that meter 10 is a wide range meter capable ofmetering over a voltage range from 96–528V. The components which enhancesuch a wide range meter include the divider network 12A–12C, which aspreviously noted are connected to receive the voltage component. Thedividers generate a divided voltage, wherein the divided voltage issubstantially linear voltage with minimal phase shift over the widedynamic range, i.e. 96–528 Volts. A processing unit (processors 14 and16) are connected to receive the divided voltage and the currentcomponent. The processing unit processes the divided voltages and thecurrent components to determine electrical energy metering values. Itwill be appreciated from the following description that processors 14and 16 require stable supply voltages to be operable. A power supply,connected to receive the voltage component and connected to processors14 and 16, generate the necessary supply voltages from the Phase Avoltage component over the wide dynamic range. Power supply 20 couldalso run off of phase B and phase C voltages or a combination of theabove. However, a combination embodiment would require additionalprotection and rectifying components.

In relation to the preferred embodiment of meter 10, currents andvoltages are sensed using conventional current transformers (CT's) andresistive voltage dividers, respectively. The appropriate multiplicationis accomplished in a new integrated circuit, i.e. processor 14.Processor 14 is essentially a programmable digital signal processor(DSP) with built in multiple analog to digital (A/D) converters. Theconverters are capable of sampling multiple input channelssimultaneously at 2400 Hz each with a resolution of 21 bits and then theintegral DSP performs various calculations on the results. For a moredetailed description of Processor 14, reference is made to U.S. Pat. No.5,555,508, which is incorporated herein by reference and which is ownedby the same assignee as the present application.

Meter 10 can be operated as either a demand meter or as a time-of-use(TOU) meter. It will be recognized that TOU meters are becomingincreasingly popular due to the greater differentiation by whichelectrical energy is billed. For example, electrical energy meteredduring peak hours will be billed differently than electrical energybilled during non-peak hours. As will be explained in greater detailbelow, first processor 14 determines units of electrical energy whileprocessor 16, in the TOU mode, qualifies such energy units in relationto the time such units were determined, i.e. the season as well as thetime of day.

All indicators and test features are brought out through the face ofmeter 10, either on LCD 30 or through optical communications port 40.Power supply 20 for the electronics is a switching power supply feedinglow voltage linear supply 22. Such an approach allows a wide operatingvoltage range for meter 10.

In the preferred embodiment of the present invention, the so-calledstandard meter components and register electronics are for the firsttime all located on a single printed circuit board (not shown) definedas an electronics assembly. This electronics assembly houses powersupplies 20, 22, 24 and 28, resistive dividers 12A–12C for all threephases, the shunt resistor portion of 18A–18C, oscillator 34, processor14, processor 16, reset circuitry, EEPROM 35, oscillator 32, opticalport components 40, LCD 30, and an option board interface 38. When thisassembly is used for demand metering, the billing data is stored inEEPROM 35. This same assembly is used for TOU metering applications bymerely utilizing battery 26 and reprogramming the configuration data inEEPROM 35. The additional time-of-use billing data is stored in theinternal RAM of processor 16, which RAM is backed by battery 26.

Consider now the various components of meter 10 in greater detail.Primary current being metered may be sensed using conventional currenttransformers. The shunt resistor portion of devices 18A–18C are locatedon the electronics assembly.

The phase voltages are brought directly to the electronic assembly whereresistive dividers 12A–12C scale these inputs to processor 14. In thepreferred embodiment, the electronic components are referenced to thevector sum of each line voltage for three wire delta systems and toearth ground for all other services. Resistive division is used todivide the input voltage so that a very linear voltage with minimalphase shift over a wide dynamic range can be obtained. This incombination with a switching power supply allows the wide voltageoperating range to be implemented.

Referring briefly to FIG. 2, each resistive divider consists of two 1Meg, 1/2 watt resistors 50/52, 54/56 and 58/60, respectively. Resistors50–60 are used to drop the line voltage at an acceptable watt loss. Eachresistor pair feeds a resistor 62, 64 and 66, respectively. Resistors62–66 are metal film resistors having a minimal temperature coefficient.This combination is very inexpensive compared to other voltage sensingtechniques. Resistors 50–60 have an operating voltage rating of 300 Vrmseach. These resistors have been individually tested with the 6 kV IEEE587 impulse waveforms to assure that the resistance is stable and thatthe devices are not destroyed. Resistors 62–66 scales the input voltageto be less than 1 Volt peak to peak to processor 14. Resistors 62–66should be in the range of from about 100 ohms to about 1 K ohms toassure this maximum voltage and maintain maximum signal.

On grounded, three wire delta systems, those components of theelectronics assembly operating on logic voltage levels (including thebattery connector) can be at an elevated voltage. In such situations,the two, 1 Meg resistor combinations (50/52, 54/56, 58/60) providecurrent limiting to the logic level electronics. The worse case currentoccurs during testing of a 480 V, 3 wire delta meter with single phaseexcitation.

It will be appreciated that energy units are calculated in processor 14primarily from multiplication of voltage and current. The preferredembodiment of processor 14, referenced above as being described in U.S.Pat. No. 5,555,508, includes three analog to digital converters. Thenecessity for three converters is primarily due to the absense ofvoltage transformers, present in prior meters.

The M37428 microcontroller 16 is a 6502 (a traditional 8 bitmicroprocessor) derivative with an expanded instruction set for bit testand manipulation. This microcontroller includes substantialfunctionality including internal LCD drivers (128 quadraplexedsegments), 8 kbytes of ROM, 384 bytes of RAM, a full duplex hardwareUART, 5 timers, dual clock inputs (32.768 kHz and up to 8 MHz), and alow power operating mode.

During normal operation, processor 16 receives the 4.1472 MHz clock fromprocessor 14 as described above. Such a clock signal translates to a1.0368 MHz cycle time. Upon power fail, processor 16 shifts to the32.768 kHz crystal oscillator 32. This allows low power operation with acycle time of 16.384 kHz. During a power failure, processor 16 keepstrack of time by counting seconds and rippling the time forward. Onceprocessor 16 has rippled the time forward, a WIT instruction is executedwhich places the unit in a mode where only the 32.768 kHz oscillator andthe timers are operational. While in this mode a timer is setup to “wakeup” processor 16 every 32,768 cycles to count a second.

Consider now the particulars of the power supplies shown in FIG. 1. Asindicated previously, the off-line switching supply 20 is designed tooperate over a 96–528 VAC input range. It connects directly to the PhaseA voltage alternating current (AC) line and requires no line frequencytransformer. A flyback converter serves as the basis of the circuit. Aflyback converter is a type of switching power supply.

As used herein, the “AC cycle” refers to the 60 Hz or 50 Hz input topower supply 20. The “switching cycle” refers to the 50 kHz to 140 kHzfrequency at which the switching transformer of power supply 20operates. It will be noted that other switching cycle frequences can beused.

Referring now to FIG. 4, power supply 20 for use in electronic metersincludes a transformer 300 having primary and secondary windings. Theinput voltage (Phase A Voltage) is provided to the primary winding sothat current may flow therethrough. As will be appreciated from FIG. 5,the secondary winding defines the output of the power supply. Referringback to FIG. 4, a switching member 302 is connected to the primarywinding of transformer 300. Switching member 302 permits and preventsthe flow of current through the primary winding. Switch member 302 isoperable in response to a control signal, which control signal isgenerated by control circuit 304. Controller 304 generates the controlsignal in response to a limit signal generated by the start/feedbackcircuit 306 in response to the output of power supply 20. Voltage clamp308 serves to limit the voltage applied to transformer 300 and switch302. Surge protection circuit 309 is provided at the input to protectagainst surges appearing in the Phase A voltage.

Referring now to FIG. 5, transformer 300 and switch 302 are shown ingreater detail. It will be appreciated that switch 302 is a transistor.At the beginning of each switching cycle, transistor 302 “turns on”,i.e. becomes conductive, and magnetizes the core of transformer 300 byapplying voltage across the primary 310. At the end of each cycle,transistor 302 turns off and allows the energy stored in the core oftransformer 300 to flow to the output of the power supply, which“output” can be generally defined by secondary 312. Simultaneously,energy flows out of the bootstrap or tertiary winding 314 to power thecontrol circuitry 304.

Feedback circuit 306 and controller 304 control the output of powersupply 20 by varying the ON time of transistor 302. Controller 304 willbe described in greater detail in relation to FIG. 5. Transistor 302 isconnected through inverter 316 to receive the output of an oscillatorformed from inverters 318, 320 and 322. It will be recognized that suchinverters form a ring oscillator. The oscillator has a free-runfrequency of 50 KHz. The ON time of transistor 302 may vary between 200ns and 10 μs. The OFF time is always between 8 and 10 μs. Duringoperation, the bootstrap winding 314 of transformer 300 (pins 10 and 11)powers controller 304, but this power is not available until the powersupply has started. The control circuit is a current-mode regulator.

At the beginning of a switching cycle, transistor 302 is turned ON bythe oscillator output. If left alone, transistor 302 would also beturned OFF by the oscillator output. Transistor 302 remains ON until thecurrent in primary 310 of transformer 300 (pins 8 and 13) ramps up tothe threshold current level I_(th) represented as a voltage V_(th). Aswill be explained below, V_(th) is generated by feedback circuit 306.When the primary current of transformer 300, represented as a voltageV_(t) and sensed by resistor 326, ramps up to the threshold levelV_(th), pin 1 of comparator 324 terminates the ON period of theoscillator by forcing the oscillator output HIGH, which output in turnis inverted by inverter 316, shutting OFF transistor 302. Transistor 302then turns OFF until the next switching cycle. Since the V_(th)indirectly controls the ON time of transistor 302, controller 304regulates the output voltage of the power supply by comparing the sensedcurrent in transformer 300 to this threshold level.

Transistor 362 and pin 7 of comparator 326 can disable the oscillator.Transistor 362, described in greater detail in FIG. 7, disables theoscillator when the line voltage exceeds 400 volts. Comparator 328disables the oscillator when the controller 304 has insufficient voltageto properly drive transistor 302. The voltage in controller 304, VC,will be described in relation to FIG. 5.

Consider now feedback circuit 306, shown in FIG. 6. When connected tothe Phase A Voltage, resistor 330 slowly charges capacitor 332. The highvalue of resistor 330 and the 400 volt limit by voltage clamp 308 limitthe power dissipation of resistor 330. After a few seconds, capacitor332 charges above 13 volts. Transistors 334 and 336 then providepositive feedback to each other and snap ON. Controller 304 can run fortens of milliseconds from the charge stored in capacitor 332. Normally,power supply 20 will successfully start and begin to power itself inthis period. If it fails to start, transistors 334 and 336 turn OFF whenthe charge across capacitor 332 drops below 8.5 volts and capacitor 332again charges through resistor 330. This cycle repeats until the supplystarts.

With high input voltages and without resistor 338 (FIG. 5), the currentsourced by resistor 330 can hold the control and start-up circuits in adisabled state that does not recycle. When Capacitor 332 drops below 8.5volts, resistor 338 places a load on the control circuit supply. Thisload insures that the start-up circuit recycles properly with high inputvoltages.

As indicated above, when the primary current of transformer 300 sensedby resistor 326 ramps up to the threshold level V_(th), pin 1 ofcomparator 324 can terminate the ON period of the oscillator. When thevoltage on capacitor 332 is less than 13 volts, zener diode 340 providesno voltage feedback. Under these conditions, the base-emitter voltage oftransistor 336 sets the current threshold I_(th) to about 650 mA. Thismaximum current limit protects transistor 302, as well as thosetransistors in voltage clamp 306, and prevents transformer 300 fromsaturating.

As the voltage on capacitor 332, which is representative of the outputvoltage of the supply, approaches the proper level, zener diode 340begins to conduct and effectively reduces the current threshold, i.e.effectively reduces V_(th). Each switching cycle will then transfersless power to the output, and the supply begins to regulate its output.

When the regulating circuitry requires ON times of transistor 302 lessthan about 400 ns, the current sense circuitry does not have time toreact to the primary current of transformer 300. In that case, theregulating circuit operates as a voltage-mode pulse width modulator.Resistor 342 (FIG. 5) generates a negative step at pin 3 of comparator324 at the beginning of each switching cycle. The regulator feedbackvoltage at pin 2 of comparator 324, which contains little currentinformation at the beginning of each switching cycle, translates thestep at pin 3 into various input overdrives of comparator 324, therebydriving the output of comparator 324 to a logic HIGH level. Thepropagation time of the comparator 324 decreases with increasingoverdrive, i.e. as the negative step increases, and the circuit acts asa pulse width modulator. The negative step will increase due to thechanging level of V_(th).

Any leakage inductance between the bootstrap winding (pins 10 and 11 oftransformer 300) and the output winding (pins 3 and 4 of transformer300) causes inaccurate tracking between the voltage on capacitor 332 andthe output voltage of the supply. This leakage inductance can cause poorload regulation of the supply. The bootstrap and output windings arebifilar wound; they are tightly coupled, have little leakage inductance,and provide acceptable load regulation. Since the two windings are indirect contact, the bootstrap winding requires Teflon insulation to meetthe isolation voltage specifications. A 100% hi-pot test duringmanufacture insures the integrity of the insulation.

Consider now the details of voltage clamp 308, shown in FIG. 7. A 528VAC input corresponds to 750 VDC after rectification. Switchingtransistors that can directly handle these voltages are extremelyexpensive. By using the voltage clamp of the present invention,relatively inexpensive switching transistors can be utilized.

In power supply 20, the switching member 302 is shut down during partsof the AC cycle that exceed 400 volts. The switching transistor,transistor 302, in conjunction with two other transistors 344 and 346,can hold off 750 VDC. During surge conditions, these three transistorscan withstand over 1500 volts. In the preferred embodiment, transistors302, 344 and 346 are 600-volt MOSFETs.

Because high-voltage electrolytic capacitors are expensive and large,this voltage clamp 308 has no bulk filter capacitor after the bridgerectifier 348. Without a bulk filter capacitor, this switching convertermust shut down during parts of the AC cycle. It intentionally shuts downduring parts of the AC cycle that exceed 400 volts, and no input poweris available when the AC cycle crosses zero. The 2200 μF outputcapacitor 350 (FIG. 5), provides output current during these periods.

As discussed above, transistors 344 and 346 act as a voltage clamp andlimit the voltage applied to switching member 302. At a 528 VAC linevoltage, the input to the clamping circuit reaches 750 volts. Duringlightning-strike surges, this voltage may approach 1500 volts. When thevoltage at the output of bridge rectifier 348 exceeds 400 volts, zenerdiodes 352 and 354 begin to conduct. These diodes, along with the 33 KΩresistors 356, 358 and 360, create bias voltages for transistors 344 and346. Transistors 344 and 346 act as source followers and maintain theirsource voltages a few volts below their gate voltages.

If, for example, the output of bridge rectifier 348 is at 1000 volts,the gates of transistors 344 and 346 will be at approximately 400 and700 volts respectively. The source of transistor 344 applies roughly 700volts to the drain of 346; the source of 346 feeds about 400 volts toswitching member 302. Transistors 344 and 346 each drop 300 volts underthese conditions and thereby share the drop from the 1000 volt input tothe 400 volt output, a level which the switching converter 302 canwithstand.

As zener diodes 352 and 354 begin to conduct and as transistors 344 and346 begin to clamp, transistor 362 turns ON and shuts down the switchingconverter. Although transistors 344 and 346 limit the voltage fed to theconverter to an acceptable level, they would dissipate an excessiveamount of heat if the switching converter 302 consumed power during theclamping period.

When switching converter 302 shuts down, transistor 302 no longer has towithstand the flyback voltage from transformer 300. Resistor 364 takesadvantage of this by allowing the output voltage of the clamp toapproach 500 volts (instead of 400 volts) as the input to the clampapproaches 1500 volts. This removes some of the burden from transistors344 and 346.

Zener diodes 352 and 354 are off and the converter 302 runs when theoutput of bridge rectifier 348 is below 400 volts. During these parts ofthe AC cycle, the 33 KΩ resistors 356, 358 and 360 directly bias thegates of transistors 344 and 346. The voltage drop across transistors344 and 346 is then slightly more than the threshold voltages of thosetransistors along with any voltage drop generated by the channelresistance of those transistors.

During the off time of transistor 302, about 10 μS, the 33 KΩ resistorscan no longer bias the gates of transistors 344 and 346. Diode 366prevents the gate capacitance of transistors 344 and 346 and thejunction capacitance of zeners 368 and 370 from discharging whentransistor 302 is off. This keeps transistors 344 and 3460N and ready toconduct when transistor 302 turns ON at the next switching cycle. If thegates of transistors 344 and 346 had discharged between switchingcycles, they would create large voltage drops and power losses duringthe time required to recharge their gates through the 33 KΩ resistors.

In the preferred embodiment, two 33 KΩ resistors are used in series toobtain the necessary voltage capability from 966 surface-mount packages.

This power supply must withstand an 8 KV, 1.2×50 μS short-branch test.Varistor 372, resistors 374, 376 and 378, and capacitor 380 protect thepower supply from lightning strike surges.

A 550 VAC varistor 372 serves as the basis of the protection circuit. Ithas the lowest standard voltage that can handle a 528 VAC input. Thedevice has a maximum clamping voltage of 1500 volts at 50 amps.

A varistor placed directly across an AC line is subject to extremelyhigh surge currents and may not protect the circuit effectively. Highsurge currents can degrade the varistor and ultimately lead tocatastrophic failure of the device. Input resistors 374 and 376 limitthe surge currents to 35 amps. This insures that the clamping voltageremains below 1500 volts and extends the life of the varistor to tens ofthousands of strikes.

Resistor 378 and capacitor 380 act as an RC filter. The filter limitsthe rate of voltage rise at the output of the bridge rectifier. Thevoltage clamping circuit, transistors 344 and 346, is able to track thisreduced dv/dt. Current forced through diodes 382, 384 and capacitor 386(FIG. 5) is also controlled by the limited rate of voltage rise.

Resistors 374 and 376 are 1 watt carbon composition resistors. Theseresistors can withstand the surge energies and voltages. Resistor 378 isa flame-proof resistor that acts as a fuse in the event of a failure inthe remainder of the circuit.

The values of resistors 374, 376 and 378 are low enough so that they donot interfere with the operation of the power supply or dissipateexcessive amounts of power.

Finally it is noted that resistors 388 and 390 act to generate the powerfail voltage PF.

By using the wide voltage ranging of the invention, a single meter canbe used in both a four wire wye application as well as in a four wiredelta application. It will be recognized that a four wire deltaapplication includes 96V sources as well as a 208V source. In the pastsuch an application required a unique meter in order to accommodate the208V source. Now all sources can be metered using the same meter used ina four wire wye application.

While the invention has been described and illustrated with reference tospecific embodiments, those skilled in the art will recognize thatmodification and variations may be made without departing from theprinciples of the invention as described herein above and set forth inthe following claims.

1. An electric energy meter for measuring electrical energy usage over awide dynamic range of standard service voltages, wherein the electricalenergy meter is used by an electric utility for customer billingpurposes, and wherein the electrical energy meter can be connected to apolyphase electrical service to measure electrical energy on more thanone phase, the meter having a power supply comprising: a transformerhaving first, second, and third windings, the power supply being capableof receiving any input voltage within the wide dynamic range of standardservice voltages, which input voltage is provided to the first windingso that current flows through the first winding, wherein a voltageacross the second winding defines an output of the power supply, whereina voltage across the third winding defines a sense signal that isrepresentative of the output of the power supply, and wherein the outputis regulated based at least in part on the sense signal to provide apredetermined output voltage independent of the input voltage, andwherein the wide range of service voltages include RMS voltages betweenabout 96 Vrms and about 528 Vrms.
 2. The electric energy meter of claim1, wherein the third winding is substantially similar to the secondwinding, so the voltage across the third winding is similar to thevoltage across the second winding.
 3. The electric energy meter of claim2, further comprising: a switching member connected to the firstwinding; a controller connected to the switching member and to the thirdwinding, wherein the controller receives the sense signal from the thirdwinding and sends a control signal to the switching member based on thesense signal, and wherein the control signal opens and closes theswitching member to permit and prevent a flow of current to the firstwinding and to regulate the output of the power supply on the secondwinding.
 4. The electric energy meter of claim 3, wherein the controlsignal operates to disable the switch means.
 5. The electric energymeter of claim 3, wherein the switching means comprises a firsttransistor, connected between the first winding and ground, and whereinthe control means comprises an oscillator, connected to the base of thetransistor, for generating an oscillating signal for switching thetransistor on and off, wherein the control signal causes the output ofthe oscillator to disable the first transistor.
 6. The electric energymeter of claim 5, wherein the first transistor comprises a 600 voltMOSFET device.
 7. The electric energy meter of claim 5, wherein theoscillator comprises a ring oscillator.
 8. The electric energy meter ofclaim 3, wherein the control means comprises an over current protectiondetector and a means for voltage protection control.
 9. The electricenergy meter of claim 8, wherein the control signal is generated inresponse to an output of one of the over current protection detector andthe means for voltage protection control.
 10. The electric energy meterof claim 3, further comprising voltage clamping means, connected to thetransformer and the switch means, wherein the input voltage is appliedto the voltage clamping means, for limiting the voltage applied to thetransformer.
 11. The electric energy meter of claim 10, wherein theclamping means comprises first and second transistors and biasing means,connected to the first and second transistors, wherein the biasing meansbiases the first and second transistors so that the voltage provided bythe clamping means does not exceed a desired level.
 12. The electricenergy meter of claim 11, wherein the clamping means disables the switchmeans when the input voltage exceeds the desired level.
 13. The electricenergy meter of claim 1, further comprising a charge means, connected tothe second winding, for storing an electrical charge when current isflowing through the first winding and for discharging stored electricalcharge when current flowing through the first winding is interrupted.